Method of and apparatus for concentrating sewage sludges



Oct. V28, 1952 Q KRAU? 2,615,842

METHOD OF' AND APPARATUS FOR CONCENIIRATING SEWAGE SLUDGES Filed OCT.. 24, 1946 2 Sl-iEETS-SHEET 1 Tanz? l.. 4s. KRAus METHOD oF AND APPARATUS FOR CONCENTRATING sEwAGr: sLuDGEs Filed oct. 24, z'sHEETs-SHEET 2 EAU atenteci ct. 28, 1952 UNITED STATES PATENT OFFICE METHOD OF AND APPARATUS FOR CONCEN- TRATING SEWAGE SLUDGES Leon S. Kraus, Peoria, Ill. Y

Application October 24, 1946, Serial No. 705,269

` claims. (ci. 21o- 2) This invention relates to a method of, and apparatus for, concentrating sewage sludges Y to solids concentrations unattainable by normal or usual settling methods.

In the various methods now used for treating sewage by biological oxidation, particularly in the activated sludge process, much difiiculty and cost is encountered in the final disposition of the sludge due to its dilute character, this being one of the most serious objections to the use of such methods.` As an example, one of the most simple methods of sludge disposal is barging the liquid material to sea. It is evident that in this procedure the barge capacity required is inversely proportional to the solids concentration of the sludge resulting from the sewage treatment process. Thus if a sewage treatment-works requires two barge volumes per day with a waste sludge concentration of three percent solids, but one barge volume per day, only, is required if the waste sludge concentration is increased to six percent solids. Y

Likewise where sludge is dried on sludge drying beds as practiced, a much higher solids concentration of sludge would require less evaporation of water than one of low solids concentration. Thus a sludge containing six per cent solids concentration contains 51.6 per cent less water per pound ofv dry solids than a 3 per cent solids concentration sludge.

The object of this invention in View of the above is to produce a more concentrated sludge than is now obtained in the usual sewage treatment processes, by which to reduce the cost of treatment and increase the facility of sludge disposal.

This object is attained in the following manner: Sewage sludges containing ammonia are aerated in the presence of a proper concentration of nitrifying organisms such as are found in sludges resulting from biological oxidations until the ammonia nitrogen is wholly or partially converted into nitrite and nitrate nitrogen. The resulting nitrified sludge is then allowed to become quiescent in a settling chamber where the solids settle to thebottom. As denittrification proceeds such solids arise to the surface of the liquid bulk to rest thereon as a floating layer.

It is found that the sludge in the floating layer attains a considerably higher solids concentration than results in normal settling methods.

Again it is found that the solids concentration of sludge in the floating layer has a minimum density at the bottom thereof while there is a maximum density at the'top of such layer.

Further, the denitriiication process can ibe accelerated by adding to nitrii'led sludge a sewage sludge that has been through biological oxidation treatment.

Since the invention involves a method as well as apparatus for practicing the method the drawings herewith provided, and forming part hereof, will assist the understanding of the whole.

Figure 1 is a iiow chart indicating the various parts of the apparatus employed.

Figure 2 is likewise a ow chart showing a different arrangement of the apparatus together with designation of ow direction as a variation from that of Figure 1.

Figure 3is a Vertical section of a receiver for flowable material, and apparatus mounted thereon including a screw conveyor.

Figure 4 is an enlarged detail in plan of parts shown in Figure 3.

Figure 5 is a detail in elevation of a conveyor as viewed from one end, and

Figure 6 is an enlarged detail in sectional elevation of the structure, also shown in Figure 3.

'In the specification the following terms are used in the appended meanings:

Digested sludge-Any liquid resulting from the methane or anaerobic fermentation of organic materials which contain suspended solids and which may be withdrawn from any part of a digestion chamber. l

Sewage-Any waste aqueous liquid containing settleable, dispersed, colloidal or dissolved organic materials or any combination of these materials.

n NitfLcation.-The process of converting ammonia nitrogen into nitrite and nitrate nitrogen by biological oxidation.

Denitrijcatz'on.-The process of converting nitrite and nitrate nitrogen to gaseous nitrogen by biochemical means.l

The procedure and method by which this process may be carried out is made apparent from the following and by a study of the gures of the drawings whereinno valves, or pumping means are shown, however, since well understood.

In Figure 1 raw sewage coming from the sewers is discharged through conduits I and I into a preliminary settling tank 2 wherein the settl'eable solids largely settle to the bottom, the eluent from said tank flowing through a conduit 3 to a tank 4 for'any usual well known biological oxidation treatment. The biological oxidized eilluent from said tank 4 iowsv through a conduit`5 to a final settling tank 6 for final removal of settleable solids, the clarified eluent from the said iinal settling tank being discharged through a conduit 7 for disposal in any desired manner.

The sludge removed from said tank. 6-

iS isi Y charged through a conduit 8 partly to the named preliminary settling tank 2 through the conduits 8 and i', and partly to inuent to a sludge nitrifying aeration tank l 5 through conduits I6, il and lli. In the activated sludge process part of the iinal settling tank sludge is discharged from said conduit 8 and conduit Iii into the conduit 3 and thence into the biological oxidation treatment tank fi.

Settled sludge from the bottom of the preliminary settling tank 2 is discharged through conduit H to a sludge digestion tank I2 wherein the sludge solids are subjected to methane fermentation known as digestion, and wherein said solids are stabilized so that they may be disposed of without nuisance odors. In some instances the sludge from the nal settling tank may not be discharged into the preliminary settling tank 2 but instead may be discharged through conduit i3 into conduit li and thence into the digestion tank l2. In the conventional procedure as usually practiced the digested sludge is withdrawn from the digestion tank l2 for iinal disposal.

As practiced herein, however, the digested sludge from said digestion tank I2 is discharged through conduit hi to the inuent to the named sludge nitrifying aeration tank l5. Simultaneously sludge from the nal settling tank 6 is added to the inuent of the sludge concentration tank through the conduits 8, i6, Il and I4 together with efiiuent from the biological oxidation treatment tank d through conduits Il and lli. In addition, part of the eiuent from the sludge nitrifying aeration tank is passed through conduit i8 back into the influent of said sludge nitrifying aeration tank. The various materials added to the influent to the sludge nitrifying aeration tank are so proportioned that the suspended solids concentration in the contents of thatI tank are maintained at a level less than 10,000 p. p. m., having as the object of the treatment therein to convert part of the added ammonia nitrogen to nitrate and nitrite nitrogen. This is brought about by the nitrirying bacteria in the iinal settling tank sludge and the biological oxidation treatment eliuent and the presence of dissolved oxygen which is supplied by adequate aeration, i. e., until part or all of the ammonia nitrogen is converted into nitrate and nitrite nitrogen.

That part of the eiiiuent from the sludge nitrifying aeration tank no1; recirculated through conduit i8 passes through conduit is into a sludge concentration tank 26, the concentrated sludge being discharged through conduitI 2l for nal sludge disposal. This sludge disposal may be accomplished by any of the well known means, namely; digestion followed by drying on sludge drying beds, digestion followed by barging to sea, digestion followed by filtration, digestion followed by filtration and subsequent drying or incineration of the lter cake, digestion and discharge to lagoons, barging to sea, drying on drying beds, iiltration and subsequent drying or incineration of the filter cake, and discharge to lagoons.

The sludge concentration tank effluent passes to the influent of the preliminary settling tank 2 through conduits 22 and i.

In order to accelerate the denitrication of the nitrite and nitrate nitrogen, and thus accelerate the floating of the sludge solids, part of the nal settling tank sludge may be passed through conduit il and discharged into conduit i9 where it mixes with the effluent from the sludge nitrifying 4 aeration tank. This is necessary where the retention period in the sludge nitriiying aeration tank is sufcient to permit a high degree of nitrication.

In Figures 3, e, 5 and 6 the structure of the sludge concentration tank 2D is shown. Said tank in this instance is made of concrete, Central of its containing space is a well 25', a pedestal 262 being erected centrally of said well. Supported upon and adapted to turn about the pedestal is one end of a platform 22' reaching across the tank. Mounted upon the platform is a power arrangement 23, a shaft 2li of which carries a supporting wheel 25 adapted to rest upon and travel upon and around a track 25 on the tank wall, the whole supporting the platform at its free end.

Suitably suspended from the platform is a housing 25 carrying within it a screw conveyor 26. said conveyor at one end overhanging the central well 23. Mounted upon the platform is a power member 2 a sprocket wheel 23 of which, through a chain 29, drives the Wheel 29' of said conveyor.

At each of the two opposite sides of the tank, outside the same, is a receiver separately identified by 3i] and 3l. Extending into the receiver B is the pipe IQ shown in Figure l. In a wall of said receiver is an inlet port 32 leading into the containing space of said tank 2S, there being a baille 35 suspended at said port and within said space.

t the opposite receiver 3i is a port 34 leading from the tank, said port having thereat within such receiver a vertically adjustable weir 35 for governing the level of material within the named tank 2e and its now therefrom. A baiiie 36 depends from the position of the named port 3e, within said tank space. Leading from the receiver 3l is the conduit 22 shown in Figure l.

Within the central well 29 is a pipe 3l leading from the said tank space, and provided with a control valve 38. Also, leading from said well is a pipe 2l identified in Figure l by the saine reference character.

Operation of the ow of material through the Sludge concentration tank 2B is indicated in Figure 3` The effluent from the sludge nitrifying aeration tank passes through conduit i9 into said concentration tank into the receiver 3a and through iniiuent port 32, the nitried sludge being diverted directly downward by the bafile 33. As denitrification takes place with the attendant liberation oi small bubbles of gaseous nitrogen the solids rise to the surface forming a floating layer of concentrated sludge. As the liquid passes toward the outlet from the tank the solids by arising are thus largely removed. The remaining liquor passes under and behind the baiiie 36 and out through the eiiiuent port 3:3, over the adjustable weir 35, discharging into the receiver 3l, leaving the same through the conduit 22.

The rotating screw conveyor 26 carried and swung over the tank by the rotating platform 22 gathers the floating layer and discharges it into the central well 2G', passing through the .pipe or conduit 2l for nal disposal. rEhe pipe 31 and valve 33 are provided for the occasional removal of bottom sludge from the tank 2G, and also for draining the same.

In Figure 2 a modied activated sludge process may be used wherein the sludge nitriiying aeration tank answers a dual purpose; first to control the settlability of the activated sludge, and second, to provide a nitriiied sludge for sludge con` centration. A

As in Figure l the raw sewage from the 'sewers moves through a conduit I2 into the preliminary settling tank 2' wherein the settleable solids are largely removed as a sludge from the bottom of said tank. The eiliuent from said tank passes through a conduit 3' and is mixed with the return activated sludge passing through a conduit lil and the mixture is discharged into aeration tank 4' wherein it is aerated for sufficient time and with sufficient air to effect the purification desired. The mixture of puried sewage and activated sludge is discharged through a conduit 5 into the final settling tank 6 wherein the activated sludge is removed from the purified sewage, the latter or final eluent, being discharged through a conduit i for nal disposal.

The activated sludge leaves `said iinal settling tank through conduit 8 and is partly returned to the aeration tanks through conduits lil and 3. Part of the activated sludge may be carried to the preliminary settling tank through conduits 8', 9' and I2 when desired.

Preliminary settling tank sludge is discharged through conduit Il into digestion tank l2 wherein the sludge partly decomposed by the anearobic methane fermentation, and the digested sludge is passed through conduit |22 into conduit 2|' where it mixes with part of the activated sludge from the final settling tank passing through the conduit 2l. This is then mixed with sludge concentration tank eluent passing through a conduit |92, the resulting mixture being discharged in the sludge nitrifying aeration tank l5' through conduit 292. The ammonia in the mixed sludges is partly converted to nitrite and nitrate nitrogen in said sludge nitrifying aeration tank, the biological action therein being accelerated by circulating the tank contents between the eiuent and influent of said tank through conduit I9. The nitried sludges leave the sludge nitrifying aeration tank through conduit 26B- and part of said effluent is discharged to the aeration tank d through conduits 26a and 3. The remaining part of the nitrified sludge is discharged to the sludge concentration tank 2% through conduits 25a and 262 wherein the sludge settles to the bottom of the tank and denitrication takes place causing the formation of small bubbles of nitrogen to become attached to the sludge particles as before described thus causing the particles to rise forming a floating layer. In order to increase the rate of denitrification part of the activated sludge passing through conduit I may be discharged into the sludge concentration tank through conduits 262 and 2Gb. This is only necessary when denitrication of the nitried sludges progresses slowly due to lack of activity of the denitrifying bacteria. The effluent from the sludge concentration tank is discharged through conduits I92 and 292 to the inuent to the sludge nitrifying aeration tank l5.

The concentrated sludge is withdrawn from the surface of the floating sludge layer and is passed through conduit 2 l2 for further treatment and disposal. In Figure 1 a pipe A supplies air to the tank l5, while in Figure 2 a pipe A for air leads to the tank l5'.

The above process aided by the drawings, has been described on the basis of continuous flow of material. Continuous iiow, however, is not essential, and in some cases is not the most desirable method of operation. It is entirely possible to operate in a step by step manner. Thus in Figure 2 the nitried sludge may be used to control the settling characteristics of the activated sludge during one period and for sludge concentration purposes during a subsequent period. It is also possible to carry out the nitrifying aeration process and the sludge concentration process as fill and draw procedure, i. e., bulk by bulk, whereby the ntrifying aeration tank may be filled over one period and the contents discharged to the sludge concentration tank in which the concentrated sludge is formed after a suiilcient period of time, and which in turn may be emptied by first withdrawing the liquor under the floating sludge layer from the bottom of the tank and then withdrawing the floating sludge layer through said bottom outlet, although this procedure would result in a less concentrated sludge than by the continuous procedure described.

In sewage treatment wherein the biologically oxidized sludge, such as activated sludge, contains nitrate and nitrite nitrogen sufficient to cause the sludge when placed in a relatively quiescent tank to rise to the surface due to denitrication, such a sludge may be concentrated to high solids concentrations by the use of the sludge concentration tank without the use of the sludge nitrifying aeration tank. In such a situation said biologically oxidized sludge may be carried directly into the sludge concentration tank, the eilluent from which is passed to the preliminary settling tanks, and the concentrated sludge passed into the digestion tanks together with the preliminary settling tank sludge. f

I claim:

1. In combination with apparatus for sewage treatment including a pipe for conveying sewage thereto, a biological oxidation apparatus, a final settling tank, and a sludge digestion apparatus, a second biological oxidation apparatus, a pipe connecting the bottom of the sludge digestion apparatus with the influent end of the said second biological oxidation apparatus so as to convey digested sludge thereto, a pipe connecting the effluent end of the latter with the influent end of the rst named biological oxidation apparatus, a pipe connected to and between the bottoni of said final settling tank and the influent end of said second biological oxidation apparatus, there being an outlet in said final settling tank for discharge of claried liquor, a sludge concentration tank, a pipe connecting the eiiluent end of the second biological oxidation apparatus with the influent end of the sludge concentration tank, a pipe connecting the eiiiuent end of the sludge concentration tank with the influent end of said second biological oxidation apparatus, and means for withdrawing concentrated sludge from said sludge concentration tank.

2. The combination with apparatus for sewage treatment including a pipe for conveying sewage thereto, a biological oxidation apparatus, a final settling tank, and a digestion tank, a nitrifying aeration tank, a pipe connecting the bottom of the digestion tank with the influent of said nitrifying aeration tank for conveying digested sludge thereto, a pipe connecting the underflow of the inal settling tank with the inuent end of said nitrifying aeration tank, a sludge concentration tank, a pipe connecting the effluent end of said nitrifying aeration tank with the influent of said sludge concentration tank, a pipe connecting the effluent end of said concentration tank with the influent end of said nitrifying aeration tank, means for withdrawing concentrated sludge from the concentration tank for discharge to the digestion tank, a pipe connecting the eiiuent end of asias@ 7 said nitrifying aeration tank with the inuent of the said biological oxidation apparatus, and a discharge pipe for clarified liquor in said final settling tank.

3. The combination with an apparatus ior sewage treatment including a biological oxidation apparatus and means for conveying sewage thereto, a iinal settling tank, a pipe `for discharging clarified liquor therefrom together with a pipe for conveying biologically oxidized sludge there-V from, and a digestion tank, of a nitrifying aeration tank, a pipe leading from the iniiuent end of the latter to the inlet for the biologically oxidized sludge to the nal settling tank, a pipe also leading from the influent end of saio` nitrifying aeration tank to the bottom of said digestion tank for conveying digested sludge to 'said nitrifying aeration tank, a sludge concentration tank, a pipe connecting the eluent end of the nitrilying aeration tank with the influent end of said concentration tank, a pipe connecting the euent end of said concentration tank with the iniiuent end of the nitriiying aeration tank, and means for conveying the concentrated sludge from the sludge concentration tank to the digestion tank.

4. The method of treating sewage which comprises the steps of settling the settieaiiie solids of raw sewage in a preliminary settling zone, passing the efluent from the primary settling zone into a biological oxidation zone, passing the eluent from the biological oxidation zone into a nal settling Zone, passing settled solids from said final settling zone to a digestion zone, passing settled solids from said digestion Zone and settled solids from said final settling zone to a anrnaanons CITED The following references are of record in the ley of this patent:

UNITED STATES PATENTS Number Name Date 1,904,916 Coombs Apr. 18, 1933 1,957,185 Weber et al. May `1', 1934 1,981,310 Currie NOV.`2G, 1934 1,986,332 Fischer Jan. i, 1935 2,027,370 Currie Jan. 14, 1935 2,102,575 Shafer Dec. 14, 1937 2,337,597 Thayer Dec. 21, 1943 2,359,004 Schlenz et al. Sept. 26, 1944 2,360,8l1 Kelly et al. Oct. 17, 1944 2,364,622 Gillard Nov. 28, 1944 2,464,223 Durdin July 16, 1946 2,419,492 Green Apr. 22, 1947 2,442,241 Kenra-o et al May 25, 1948 2,458,163 Hays Jan. 4, 1949 2,517,792 Kraus Aug. 8, 1950 

4. THE METHOD OF TREATING SEWAGE WHICH COMPRISES THE STEPS OF SETTLING THE SETTEABLE SOLIDS OF RAW SEWAGE IN A PRELIMINARY SETTLING ZONE, PASSING THE EFFLUENT FROM THE PRIMARY SETTLING ZONE INTO A BIOLOGICAL OXIDATION ZONE, PASSING THE EFFLUENT FROM THE BIOLOGICAL OXIDATION ZONE INTO A FINAL SETTLING ZONE, PASSING SETTLED SOLIDS FROM SAID FINAL SETTLING ZONE TO A DIGESTION ZONE, PASSING SETTLED SOLIDS FROM SAID DIGESTION ZONE AND SETTLED SOLIDS FROM SAID FINAL SETTLING ZONE TO A NITRIFYING ZONE, AERATING THE MIXTURE OF SETTLED SOLIDS IN SAID NITRIFYING ZONE, PASSING EFFLUENT FROM SAID NITRIFYING ZONE INTO A QUIESCENT SLUDGE CONCENTRATION ZONE WHEREIN THE SOLIDS UNDERGO DENITRIFICATION AND ACCUMULATE AT THE SURFACE IN SAID QUIESCENT ZONE AND REMOVING SAID ACCUMULATED SOLIDS. 